Area & Volume Calculator
Work out the area of a circle, triangle, rectangle or trapezoid, and the volume and surface area of a cylinder, cone, sphere or box. The formula and your numbers plugged into it are shown step by step. Pick a length unit and the area and volume units follow, such as cm² and cm³. Everything runs in your browser and nothing you enter is sent to a server. For ratios, see the Ratio & Percentage Calculator, and to convert units, try the Unit Converter.
🔒 Runs in your browser · Your data is never sent to a server
Notes
- All inputs are treated as the same length unit. If you have a mix such as mm and cm, convert them first.
- Results are rounded to 6 decimal places. Even with full-precision π, tiny floating-point errors can remain.
- Choosing 3.14 or another rounded π matches textbook and exam conventions. The steps show π as that value.
- Triangles and trapezoids show area only, and rectangles show area and perimeter. Perimeters that need slanted side lengths are not calculated.
- A cone's surface area is the base area plus the lateral area (π × r × slant height).
Glossary
Pi (π)
The ratio of a circle's circumference to its diameter, an irrational number of about 3.14159265… Rounded values such as 3.14 or 3.1416 are common, and the number of digits changes the result slightly.
Surface area
The total area of a solid's outer surface. For a cylinder it is two circles plus the side, and for a box it is the sum of the six faces.
Slant height
The slanted distance from a cone's apex to the edge of its base. It equals √(r² + h²) for radius r and height h.
Area and volume units
If you enter lengths in cm, areas come out in cm² and volumes in cm³. 1 m² = 10,000 cm², and 1 L = 1,000 cm³.
FAQ
How many digits of pi does it use?
By default it uses the double-precision pi built into JavaScript (3.141592653589793). You can choose 3.14, 3.1416 or another rounded value to match a textbook or exam, and the steps show that value.
How are the area and volume units decided?
They follow the length unit you pick: enter lengths in cm and areas are in cm² and volumes in cm³. If your lengths use mixed units, convert them to one unit first.
What happens if I enter 0 or a negative number?
A shape cannot have a length of 0 or less, so an error is shown and nothing is calculated. Decimal values are fine.
How is the surface area of a cone calculated?
It finds the slant height l = √(r² + h²), then adds the base area π r² and the lateral area π r l, giving π × r × (r + l).
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